For words that have only 3 letters, there isn't a 4th letter. For instance with the word “include”, there won't be any a lot more letters afterwards and so must be the word "add". The word “addict” is from the BIP39 wordlist however, you would have used “addi” for “addict”. https://macrobookmarks.com/story19093297/top-latest-five-bip39-words-urban-news